Closed cell sponge weatherstrips have been the standard for years to seal vehicle closures against the passage of air and moisture. The weatherstrip attaches to the vehicle body or closure around the opening (e.g. door or trunk opening). The weatherstrip preferably includes a bulbular or tubular section that is designed to provide an interference fit between the closure and body, and a mounting section to secure the weatherstrip in place. When the door or trunk lid is closed, the weatherstrip mechanically flexes according to the degree of interference. Generally, the greater the interference, the better the sealing function is obtained.
Good sealing of closures is particularly important in vehicles in order to isolate the passengers from inclement weather conditions; namely, precipitation as well as excessively hot or cold air. Since the vehicle moves through the air, it is also important to the comfort of the passengers to minimize the wind noise. It should be recognized, however, that the high degree of interference of the weatherstrip between the door and door frame required for good sealing, unfortunately increases the closing effort.
Another consideration for vehicle weatherstrip design relates to an annoying problem known as "compression shock". With the improved closure sealing, the rapid closing of a door on an otherwise closed vehicle often results in a momentary air compression in the passenger compartment. In essence, trapped air inside the compartment cannot escape past the tight weatherstrip seals around the various closures. This problem is particularly acute in designs where the closure moves substantially transverse to the body, such as in conventional swinging doors or trunk lids. This compression shock not only further increases the closing effort required, but also causes an unpleasant feeling to the passengers.
Attempts to reduce door closing effort have in the past resulted in reduced sealing efficiency. Conversely, past attempts to emphasize improved sealing have resulted in a need for excessive closing effort. Neither extreme is favored by consumers. Thus, automotive engineers have found it necessary to compromise these conflicting engineering requirements, with the best designs heretofore carefully balancing the relationship between sealing and closing effort.
Some efforts in the past have addressed the seemingly conflicting concerns and provided some limited improvement. For example, spaced bleed apertures have been formed along the entire length of weatherstrip so air is not entrapped as it is compressed inside the weatherstrip when the closure is closed. More specifically, the apertures insure that the internal air pressure is ambient at all times. Thus, mechanical flexing of the weatherstrip remains the principal design criteria for sealing with this improvement. Advantageously, by eliminating air entrapment, the closing effort for a rapidly closing door is reduced. Still, it should be recognized that this approach is not effective in improving the sealing efficiency since the interference fit is not appreciably increased.
Another idea that has gained some acceptance in the automotive industry recently is to employ at least two weatherstrips in juxtaposition to seal together when the door or lid is closed. The engaging parts of the weatherstrips are designed to form a labyrinth seal, and as a result some improved sealing is obtained. Of course, with this arrangement the degree of interference fit commensurate with easy closing is still sorely limited, and the cost of forming the seal is substantially increased.
Another approach that has been proposed for vehicles is to make the weatherstrips inflatable. The basic idea is that when the door is closed, a positive pressure (greater than ambient pressure) is applied inside the closed tubular weatherstrip to provide expansion against the door and door frame, thus providing increased interference and an improved seal. As will be recognized, this approach does reduce the door closing effort and compression shock because the non-inflated weatherstrip does not engage in an interference fit with the door and the door frame until the door is closed and the superatmospheric pressure is applied.
This concept, while useful in aircraft and aerospace vehicles presents problems when attempts have been made to adapt it to general automotive use. First, in order to provide a closure sealing system using the superatmospheric pressure concept, a sophisticated air pressure supply system that is highly reliable must be provided. This is so since if air pressure is lost, a complete failure of the sealing function results and the interior is susceptible to damage from water leakage, as well as the passengers being exposed to extremes of hot and cold atmospheric conditions and excessive wind noise. Furthermore, such a sophisticated air pressure system is relatively expensive, and thus adding such auxiliary equipment is not conducive to competitive pricing of a consumer product, such as an automobile.
Similarly, the superatmospheric inflatable weatherstrip must not lose pressure over extended periods of time. To guard against this in an automotive system where small, pin-hole leaks are inevitable, especially after several years of use, an electric pump would be required to be periodically energized to maintain the optimum sealing pressure. Such a condition would inevitably lead to the need for increased storage capacity of the electrical battery in the automobile, and under extended periods of inactivity of the automobile, complete discharge of the battery. Additionally, the superatmospheric pressure system must provide relatively sophisticated regulators to compensate for variations in ambient pressure conditions, such as due to altitude and barometric pressure variations, as well as temperature variations. Such additional cost adds to the prohibitiveness of using this type of system on a high volume consumer product, such as an automobile.